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Obesity, Diet, and Insulin Resistance in HorsesBy Kentucky Equine Research Staff · October 6, 2014

Obesity and insulin resistance (IR) are widespread conditions among domestic horses. Horses with obesity and insulin resistance are at higher than normal risk for laminitis and equine metabolic syndrome. Obesity also strains the joints and leads to exercise intolerance.

Not every obese horse is insulin resistant, and not every horse with IR is obese; however, some relationship is suspected. Likewise, some obese horses on extremely restricted diets fail to lose weight, so other factors in addition to diet must be considered.

Researchers at the University of Melbourne in Australia are investigating these facets of equine health. Summaries of the progression of these studies are given below.

  • Horses and ponies tend to have different metabolic rates. Ponies are usually somewhat stockier and have heavier bodies for their height than horses. Members of some horse breeds such as Morgans, Paso Finos, and Quarter Horses show a similar body type. A study is being conducted using Standardbred horses as a reference breed; mixed-breed ponies as a second group; and Andalusian horses as a third group. This study will look at various management factors that may contribute to the development of obesity, equine metabolic syndrome, and laminitis.
  • In a pilot study, equines in these groups were fed a fiber-based meal that included 1.5g/kg body weight of glucose. Breed did not affect glycemic response, but insulin responses of the ponies and Andalusian horses were significantly elevated compared to those of the Standardbred horses.
  • In a 20-week project, animals fed a high-calorie diet containing a once-daily glucose load became obese, as did those fed a high-calorie diet with added fat. Animals on a control diet did not become obese. Insulin sensitivity in the group given added fat did not differ from those in the control group, while insulin sensitivity improved slightly in the group fed glucose. This result indicated that obesity in itself did not necessarily cause IR.
  • To see whether a longer period of an increased insulin response would cause IR, two groups were given large grain meals twice a day while the control group did not get these meals. Ponies and Andalusians showed a greater and longer-lasting insulin response than Standardbreds, indicating decreased insulin sensitivity.

Results to this point suggest that increased insulin response and IR may tend to drive obesity in horses and ponies. Continuation of the research may shed more light on obesity and metabolism in equines.